The plural of arca in Latin, referring to multiple chests, boxes, arks, or in zoology, multiple organisms of the genus Arca (ark shells).
From Latin arca + the Latin plural suffix -e. This is the classical Latin plural form, though English often uses 'arcas' in modern usage.
Arcae is what you get when Latin plurals survive in English scientific terminology—it's a reminder that international science still speaks partially in Latin, creating these odd hybrid sentences where English words suddenly become Latin halfway through.
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